A splash of green paint was discovered at the base of the 19-foot statue of President Abraham Lincoln and on the Civil War-era president's lap shortly after 1 a.m. ET Friday, U.S. Park Police say. Crews continue to clean the statue and the chamber where Lincoln sits, but police now are allowing visitors to go to the top of the steps.

"Honestly, from a personal level it breaks my heart that somebody would do this, especially this year, the 50th anniversary of the March on Washington," said Carol Johnson, a U.S. Park Service spokeswoman. On Aug. 28, 1963, the Rev. Dr. Martin Luther King Jr. stood on the steps of the Lincoln Memorial to deliver his I Have A Dream speech during the March on Washington.

The paint did not permanently damage the memorial, Park Police said in a press release.

Construction on the Lincoln Memorial was begun in 1914 on land that was part of the Potomac River when Lincoln was president. The monument was dedicated in 1922 and is now listed on the National Register of Historic Places.

Investigators are reviewing video from seven surveillance cameras mounted around the memorial to help determine who committed the crime. The memorial, like all memorials on the National Mall, is open 24 hours a day.

"I think it's really sad," said one visitor, who came from Tennessee with her children to view the statue but was unable to get in.

The National Parks Foundation, a private group chartered by Congress in 1967 that supports the National Park Service, is encouraging donations to help clean up vandalism at the Lincoln Memorial and the more than 400 other national parks across the country that often are vandals' targets.

Texting the word PARKS to 90999 will add a one-time $10 donation to your phone bill. Logging onto the foundation's website, will allow you to make a donation in other amounts and have the gift matched up to $50,000. Tweet about your efforts using the #RespectLincoln hashtag.